NOTE: As of Spring 2.0, this class requires Commons FileUpload 1.1
or higher. The implementation does not use any deprecated FileUpload 1.0 API
anymore, to be compatible with future Commons FileUpload releases.

transferTo

This may either move the file in the filesystem, copy the file in the
filesystem, or save memory-held contents to the destination file.
If the destination file already exists, it will be deleted first.

If the file has been moved in the filesystem, this operation cannot
be invoked again. Therefore, call this method just once to be able to
work with any storage mechanism.